1. Field of the Invention
The present invention relates to a magnetic drive apparatus, and more particularly to a driving apparatus that does not require driving force through coils.
2. Description of the Related Art
In a driving apparatus using magnetic force, an electric current is usually supplied to the excitation coils to generate magnetic force that rotates the rotor magnets. When this driving apparatus is used, for example, as the driving source of a clock, a stepping motor with the configuration described above is driven intermittently based on the reference signal generated by a quartz oscillator (for example, see Japanese Patent Laid-Open Publication No. 2002-90473).
One of the problems with a magnetic drive apparatus, in which the excitation coils described above are used, is that it is difficult to provide high energy efficiency because there is a copper loss generated when the driving current flows through the excitation coils and therefore difficult to reduce the power consumption.
The size of a magnetic drive apparatus, in which excitation coils are used, is limited by the coil diameter. Therefore, a compact, low profile magnetic drive apparatus requires that the coil diameter be small. Therefore, another problem in this case is that, because a smaller coil diameter results in a reduction in the torque, the magnetic drive apparatus must be larger enough to ensure a predetermined torque.
As described above, a conventional magnetic drive apparatus has problems caused by excitation coils used in the driving part; for example, the problems include the limitation on the amount of magnetic flux due to power consumption and magnetic saturation and the limitation on size reduction and low-profile design due to the coil diameter.
In view of the problems described above, a driving apparatus is proposed in which magnetic switching elements are used to open and close the flow of the magnetic flux of a permanent magnet into the stator (for example, Japanese Patent Laid-Open Publication No. Sho 54-126917).
As described above, a magnetic drive apparatus, in which excitation coils are used as the driving source, has problems caused by excitation coils used as the driving source, for example, large power consumption and the limitation on size reduction and low-profile design due to the coil diameter.
To solve this problem, Patent Document 2 discloses a driving method for on/off controlling the magnetic flux using magnetoresistance switching elements instead of the coil driving method. However, this driving method uses coils as the magnetic resistance switching elements and, therefore, does not give the full effect of power saving, size reduction, and low-profile design. Even if magnetic resistance switching elements that do not use coils are used, the flow of the magnetic flux to the rotor is switched simply in two directions because whether the magnetic flux of a permanent magnet is supplied to the stator is on/off controlled in the configuration proposed in Patent Document 2. The problem with this magnetic flux switching is that it is difficult to change the driving direction freely and to perform smooth driving control.
Another problem is that, because the magnetic flux is not supplied to the rotor but is returned to the permanent magnet when the magnetic flux is switched, the magnetic flux does not contribute to the driving of the rotor and thus does not fully achieve high driving efficiency.